Support assembly for a low-wattage cathode



c. s. SZEGHO 3,333,138

SUPPORT ASSEMBLY FOR A LOWWATTAGE CATHODE July 25, 1967 Filed Jan. 11, 1965 INVENTOR. 3 9

coiz t anz in United States Patent 3,333,138 SUPPORT ASSEMBLY FOR A LOW-WATTAGE CATHODE Constantin S. Szegho, Chicago, Ill., assignor to The Rauland Corporation, Chicago, 111., a corporation of Illinois Filed Jan. 11, 1965, Ser. No. 424,641 6 Claims. (Cl. 313-270) ABSTRACT OF THE DISCLOSURE A low-wattage cathode for a television picture tube or the like is mounted within a surrounding heat shield by several straps each of a configuration and composition to minimize thermal loss therethrough while providing necessary cathode support. Preferably, the ends of each strap are fastened respectively at the lower end of the cathode sleeve and at the upper end of the cathode shield and are of a hair-pin like shape.

This invention relates generally to electron discharge devices and more particularly to cathode assemblies therefor having extremely low power input requirements.

In discharge devices for use in a variety of environments it is often a prime consideration to provide an eflicient cathode geometry wherein the maximum amount of electron emission can be produced with a minimum amount of input power. For example, with the practical advent of transistors for use in television receivers, it has become both feasible and desirable to provide a portable receiver which operates from a self-contained battery pack. However, the relatively large amount of power, ranging from three to four watts or more, consumed by conventional picture tube cathodes compels the use of expensive, cumbersome battery supplies while permitting of only undesirably short operating periods between recharging of the batteries.

To obviate this and similar difficulties, cathode efficiencies have been improved by such methods as providing more effective heating elements, surrounding the cathode with a reflective heat shield, and employing cathode supports utilizing members of a low thermal conductivity which contact the cathode structure only along a minimum surface area. The latter measure tends to reduce the troublesome heat sink effect of the elements supporting the cathode structure. Unfortunately, however, conductive heat loss via the cathode mounting assembly still has been found to be excessive.

It is therefore an object of this invention to provide a new and improved cathode assembly for an electron discharge device.

It is another object of the invention to provide a cathode assembly that substantially reduces conductive heat loss from the cathode structure of a television picture tube.

It is a further object of this invention to provide an improved miniature cathode structure that efliciently utilizes the input power.

Accordingly, the invention is directed to a low wattage cathode assembly of an electron discharge device comprising a hollow metallic cylindrical cathode sleeve member having a lower end portion and an upper end terminating in a metallic cap portion having electron emissive material deposited thereon, and further including a hollow metallic cylindrical cathode heat shield, having upper and lower open end portions, disposed coaxially with the sleeve member and spaced therefrom. In accordance with the invention, the means for mounting the sleeve member within the heat shield consists essentially of a plurality of substantially rigid support members of low thermal conductance, each having one end fixed to the 3,333,138 Patented July 25, 1967 "ice lower end of the sleeve member and another end fixed to the upper end portion of theshield, and each having an intermediate section longer than the distance between the lower end portion of the sleeve member and the upper end portion of the shield. The intermediate sections of these support members are also spaced from the sleeve member and the shield and at least partially extend through the annular space therebetween.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a longitudinal view, partly in section, of a portion of an electron gun assembly of a cathode-ray tube embodying a cathode assembly constructed according to the invention;

FIGURE 2 is a. cross-sectional view taken along lines 22 of FIGURE 1;

FIGURE 3 is an enlarged longitudinal section of the cathode assembly taken along lines 3-3 of FIGURE 2; and

FIGURE 4 is a perspective view illustrating a modified embodiment of the invention.

Referring now to FIGURE 1, there is shown a cathodecontrol grid assembly 10 of, for example, a picture tube of a portable television reeciver. The assembly 10 may be fitted within the picture tube in a manner well-known in the art and includes a cylindrical control grid cup 12 provided with an end closure wall 14 having a central electron beam aperture 15 therein. A cathode sleeve member having a cap portion bearing electron emissive material is disposed within control grid 12, closely adjacent grid aperture 15, and is aligned coaxially therewith. As will presently be explained in greater detail, sleeve member 17 is supported within and is spaced from a similarly coaxially aligned heat shield 20 by a plurality of subst-antially rigid support members 22, a portion of some of which are shown protruding below shield 20 in FIG- URE 1. Shield 20 is in turn mounted within the discharge device, and more specifically as here shown, within grid cup 12 by a circular insulative bushing 24 having a central opening for receiving shield 20. Crimped portions 26, 27 .of the shield retain it firmly within ceramic support 24. The subassembly thus formed is held a predetermined distance from the closure wall 14 of the control electrode 'by a cylindrical cathode-grid spacer washer 29. An annular flanged retaining member 31 welded to the inner circumference of grid cup 12 immediately below insulator 24 rigidly retains the subassembly in its assigned position.

As shown in FIGURE 2, insulator 24 preferably has a triangular, rather than circular, central aperture 33 for accommodating the shield to minimize cont-act area therewith and thereby lessen the heat sink effect of surrounding members. A number of other equally familiar practices may be employed to enhance the efficiency of the cathode structure; however, as will be understood these considerations are independent of the present invention.

Looking now to the detailed illustration of FIGURE 3, it is seen that cathode sleeve 17 is a hollow metal cylindrical tube having a lower end portion 35 and terminated at an upper end portion 36 by a transverse metallic cap 37. Surface 37 has electron emissive material 38, such as barium oxide and/ or strontium oxide, deposited thereon in a manner well-known in the art. As illustrated, sleeve member 17 actually is composed of a lower trunk portion, spread somewhat near its upper end to accept a closed cylindrical top which is force fitted therein. This,

however, is merely a production convenience; the sleeve member may be of unitary construction if desired;

A coiled heater 40 preferably having a high thermal conversion efficiency and other characteristics consistent with the objectives of the invention is inserted within sleeve member 17. The turns of the heater wire are closely spaced from the inner surface of cap 37 and are generally congregated near the upper end of cathode sleeve 17. The latter element is also of a predetermined short length only slightly longer than heater 40 in order to concentrate the heat within a small volume.

' As is clearly represented in FIGURE 3, cathode heat shield is of a length greater than that of sleeve 17, and consists of a hollow metal cylinder having upper and lower open end portions 39 and 41, respectively. Concentric cylinders 17, 20 are spaced from each other an amount sulhcient to permit the supporting structure now to be described, to extend through the annular space therebetween without contacting either sidewall except where fixed thereto. In'addition, the upper end.39 of heat shield 20 preferably terminates only slightly below the transverse cap surface 37 of thesleeve member. This provides maximum heat reflectivity without interfering with cathode-grid electrical characteristics and also blocks 'line-of-sight paths extending from the emissive cathode surface to the insulative bushing 24. As aproduct of this concealment of the cathode, material evaporated from its surface is effectively prevented from depositing onto ceramic washer 24 and forming an electrical leakage path between the grid and cathode. Annular trench 42 of bushing 24 further aids in this respect by shadowing a portion of the washer 24 from the effects of cathode sublimation.

The means for mounting sleeve member 17 within heat shield 20 consists essentially of a plurality of substantially rigid support members 22 of low thermal conductance, each of which is fixed to the sleeve member, as by welding, only at its lower end 35 and to shield 20 only at its upper end portion 39. Each of the supports 22 has an intermediate section at least partially extending paraxially through the annular space between concentric cylinders 17, 20 and which is longer than the distance between the lower end of the sleeve member and the upper end of the shield for precluding substantial conductive heat transfer between these elements. Further in accordance with the invention, the support members are spaced'from the sleeve member and from the shield, and despite their substantial length, the unique mounting assembly has been found to display a more than adequate strength for its intended function. More specifically, however, the inventive structure comprises a triad of elongated metallic support members at equally spaced circumferential intervals, each having one end welded to lower end portion 35 of the sleeve member and the other end thereof welded to the upper end portion 39 of heat shield 20. Preferably, the supports include substantially V-shaped segments which extend downwardly from both the heat shield and the sleeve member, as shown. To achieve the greatest benefits of the invention, the intermediate portions of the support member are made as long as possible consistent with space limitations; in any event, they are substantially longer than cathode sleeve member 17 and in most gun assemblies they may conveniently be made at least two or three times the 7 length of sleeve 17.

In the embodiment shown in FIGURE 3, member 22 consists of two cantilever sections 43 and 44 extending downwardly from the sleeve member and the heat shield,

respectively, and joined at a point 45 lying substantially below the termination of sleeve 17. However, as is apparent from the modified structure shown in FIGURE 4, member 22 may be of a unitary construction comprising, for example, three legs integral with and depending in predetermined spaced intervals from a collar portion 47 that is wrapped or press fitted upon the lower section of the supporting structure. As is apparent, the latter form is simply manufactured and also specially adapted to production techniques where the electron gun assembly is fabricated by taking advantage of the numerous concentric, self-jigging parts. Thus the gun can be easily assembled in a few steps, and the junctions of the various parts may be formed by press fitting or by spot welding in a single simultaneous operation. It has also been found helpful in production to flare the upper portion 39 of shield 20 thereby facilitating welding of members 22 to the surface thereof.

In addition to the high thermal resistance material used in the cathode mounting structure, the members thereof are made as thin as possible consistent with strength requirements in order to further increase the thermal resistance of the heat conduction path away from sleeve 17. As will also be noted, the effective length of each of the support members is further lengthened. by affixing these members only to the end of the cathode sleeve remote from the emissive cap portion. Thus, due to the unique geometry of the cathode mounting members, the heat conduction paths are much longer than in previous constructions, preferably two to three times the length of the cathode sleeve, while still within a compact volume, and. further being of a construction which has been found to provide the necessary firm support for the V color temperature of 867 C. with an input power of only .87 watt. This is to be contrasted with the'3-4 watts required for conventional cathodes, and the l-2 watt power requirements of many so-called low power cathode structures. It should also be noted that the cathode of the inventive assembly will produce satisfactory emission at 814 C., hence, by using an appropriate heater element the input power may be further reduced with no sacrifice in performance. Merely by way of illustration and in no sense byway of limitation, the materials and dimensions thereof used in the cathode-grid assembly of this tube were as follows Cathode sleeve 22:

Material Nickel or a predominantly nickel alloy, such as INCO #225 or INCO #330.

Length .125 inch.

Diameter .065 inch.

Thickness .0025 inch.

Heat shield 20:

' Material Nickel or a predominantly nickel alloy, such as V INCO #220.

Length .170 inch.

Diameter .090 inch.

Thickness .003 inch.

Insulative bushing 24:

Material Ceramic (s'teatite).

Diameter .370jinch.

Thickness .070 inch.

Heater 40 Rating 12.6 volts at 60-65 milliamps. Mounting strips 22:

Material Alloy consisting of nickel and 20% chro-' mium.

Length segment 43 .125 inch.

Length segment 44 .208 inch.

Thickness .001 inch.

Width .025 inch.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In an electron discharge device, a low-wattage cathode assembly comprising:

a hollow metallic cylindrical cathode sleeve member having a lower end portion and an upper end terminating in a metallic cap portion;

electron emissive material on said cap portion;

a hollow metallic cylindrical cathode heat shield, having upper and lower open end portions, disposed coaxially with said sleeve member and spaced therefrom; and

means for mounting said sleeve member within said heat shield consisting essentially of a plurality of substantially rigid support members of low thermal conductance each having one end fixed to said lower end portion of said sleeve member and another end fixed to one of said end portions of said shield, and said support members each having an intermediate section longer than the distance between said lower end portion of said sleeve member and said upper end portion of said shield, said intermediate sections of said support members being spaced from said sleeve member and from said shield and at least partially extending through the annular space therebetween.

2. In an electron discharge device, a low-wattage cathode assembly comprising:

a hollow metallic cylindrical cathode sleeve member having a lower end portion and an upper end terminating in a metallic cap portion;

electron emissive material on said cap portion;

a hollow metallic cylindrical cathode heat shield, having upper and lower open end portions, disposed coaxially with said sleeve member and spaced therefrom; and

means for mounting said sleeve member within said heat shield consisting essentially of a plurality of substantially rigid support members of low thermal conductance each having one end fixed to said lower end portion of said sleeve member and another end fixed to said upper end portion of said shield, and said support members each having an intermediate section longer than the distance between said lower end portion of said sleeve member and said upper end portion of said shield, said intermediate sections of said support members being spaced from said sleeve member and from said shield and at least partially extending through the annular space therebetween.

3. A cathode assembly according to claim 2, in which said intermediate portion of each of said support members includes a substantially V-shaped segment.

4. A cathode assembly according to claim 2, in which said intermediate portions of each of said support members includes a substantially V-sbaped segment extending downwardly through said annular space between said sleeve member and said shield.

5. In an electron discharge device a cathode assembly 6 having low power input requirements, comprising:

a hollow metallic cylindrical cathode heat shield having 6 upper and lower open end portions and being of a predetermined length;

a hollow metallic cylindrical cathode sleeve member disposed coaxially within said heat shield and spaced therefrom, said sleeve member being of a length less than said predetermined length and further having a lower end portion and an upper end terminating in a metallic cap portion;

electron emissive material on said cap portion; and

means for firmly supporting said cathode sleeve member within said heat shield while minimizing conductive heat transfer from said sleeve member to said heat shield, said supporting means consisting essentially of a plurality of substantially rigid elongated metallic support members of low thermal conductance extending paraxially through the annular spacebetween said sleeve and said shield at predetermined spaced intervals about the circumference thereof, each of said support members being fixed only to said lower end portion of said sleeve member and to said upper end portion of said shield and each having an intermediate portion of a length greater than said predetermined length and spaced from said sleeve member and from said shield, said intermediate portions of said support members each including a V-shaped segment extending downwardly from said sleeve member and from said shield.

6. In an electron discharge device a cathode assembly having low power input requirements, comprising:

a hollow metallic cylindrical cathode heat shield having upper and lower open end portions and being of a predetermined length;

a hollow metallic cylindrical cathode sleeve member disposed coaxially Within said heat shield and spaced therefrom, said sleeve member being of a length less than said predetermined length and further having a lower end portion and an upper end terminating in a metallic cap portion;

electron emissive material on said cap portion; and

means for firmly supporting said cathode sleeve member within said heat shield while minimizing conductive heat transfer from said sleeve member to said heat shield, said supporting means consisting essentially of a plurality of substantially rigid elongated metallic support members of low thermal conductance extending paraxially through the annular space between said sleeve and said shield at predetermined spaced intervals about the circumference thereof, each of said support members being fixed to said lower end portion of said sleeve member and to said upper end portion of said shield and each having an intermediate portion of a length greater than twice said length of said sleeve member and spaced from said sleeve member and from said shield, said intermediate portions of said support members each including a V-shaped segment extending downwardly from said sleeve member and from said shield.

References Cited UNITED STATES PATENTS 2,335,818 11/1943 Trumbull et al. 3l3-27O 2,914,694 11/ 1959 Chin 313270 3,145,318 8/1959 Paull 313-270 X 3,234,425 2/ 1966 Posner et al 313270 JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner. 

1. IN AN ELECTRON DISCHARGE DEVICE, A LOW-WATTAGE CATHODE ASSEMBLY COMPRISING: A HOLLOW METALLIC CYLINDRICAL CATHODE SLEEVE MEMBER HAVING A LOWER END PORTION AND AN UPPER END TERMINATING IN A METALLIC CAP PORTION; ELECTRON EMISSIVE MATERIAL ON SAID CAP PORTION; A HOLLOW METALLIC CYLINDRICAL CATHODE HEAT SHIELD, HAVING UPPER AND LOWER OPEN END PORTIONS, DISPOSED COAXIALLY WITH SAID SLEEVE MEMBER AND SPACED THEREFROM; AND MEANS FOR MOUNTING SAID SLEEVE MEMBER WITHIN SAID HEAT SHIELD CONSISTING ESSENTIALLY OF A PLURALITY OF SUBSTANTIALLY RIGID SUPPORT MEMBERS OF LOW THERMAL CONDUCTANCE EACH HAVING ONE END FIXED TO SAID LOWER END PORTION OF SAID SLEEVE MEMBER AND ANOTHER END FIXED TO ONE OF SAID END PORTIONS OF SAID SHIELD, AND SAID SUPPORT MEMBERS EACH HAVING AN INTERMEDIATE SECTION LONGER THAN THE DISTANCE BETWEEN SAID LOWER END PORTION OF SAID SLEEVE MEMBER AND SAID UPPER END PORTION OF SAID SHIELD, SAID INTERMEDIATE SECTIONS OF SAID SUPPORT MEMBERS BEING SPACED FROM SAID SLEEVE MEMBER AND FROM SAID SHIELD AND AT LEAST PARTIALLY EXTENDING THROUGH THE ANNULAR SPACE THEREBETWEEN. 